I say modify it. I did this in Chronopia. I have 3 Tusked Raiders. I made them a Unit. Now, if you feel they are too much, you can tone them down, they will also cost less but you then can add more of them. I did so in the thinking they were sort of like Blood Hunters (Devout). I also did the same for Firstborn mounted.
So in Warzone terms, and for units like Great Greys or Sharks, and talking about other factions, I think 2 to 3 are a good size. A squad of 1 is sort of not a squad to me. Its an Individual. So minimum 2 but I can see 2 - 3 in a unit. OR 2 - 4 might be the sweet spot so you can have 2, 3, or 4 in a squad.
Since you pay for what might not be 'not-cheap' models I don't see an imbalance. Also Considering ORCA are pimps and you can take up to like 3 of them, having those Mishima dragon riders up to 6 I don't see any reason why that is a bad idea. The 3 ORCA facing you will not be afraid of your 6 lizard riders.